Payback on Duct Insullation

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I am in the process of wrapping the forced air heating ducts in my crawl space with a material that looks like bubblewrap with foil on both sides. Does anyone have any idea of how much savings this will be on my gas bill? The insullation is rated at R6, but I cannot relate this to actual savings in energy.
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Be carefull it is not rated R6 if its the bubble wrap Im thinkng of, read it carefully, I think its a radiant barrier.
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sherwindu wrote:

getting via the ducts to begin with. If they're already insulated, I suspect you might not see enough improvement to pay for the bubblewrap stuff (if it's what I'm thinking of, it's not cheap).
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It's very difficult to even try to estimate without having any knowledge of your installation/climate.
That said, chances are that it will be noticable savings if you compare equivalent periods.
In an externally vented/drafty crawlspace, you could be losing a _lot_ of heat from the bare ducts.
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Chris Lewis wrote:

I don't see where he said they were bare ducts.
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Ducts should be sealed with mastic first, fiberglass is better than bubble crap, higher R and much cheaper. Best way is slide on duct insulation. Bubble wrap I would not waste my time with and dought if it is R 6 more likely its R 1 or less per inch
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Take the square foot surface of the duct, divide by R6, multiply by the ambient temperature, add the relative humidity and that is the percentage of your gas bill you save.
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... 70 ft^2 of R1 duct might lose (130-50)70ft^2/R1 = 5.6K Btu/h to a 50 F crawl space.

Wrapping the duct would save 70ft^2/R6x50F+50%RH = 633% of the gas bill? :-)
Wrapping the duct would reduce the heat loss to (130-50)70ft^2/R7 = 800 Btu/h.
Then again, with an airtight crawlspace above a vapor barrier, a lot of this heat could end up in the house. Maybe it's better to insulate the crawlspace.
Nick
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Everyone Assumes its R6, did anyone read packing lit with that stuff, the ratings are not certified and state " Like R 6' its a BS rating just like " Insulating ceramic paint". Its a radiant barrier, foilfaced duct R 7 fiberglass is R 7 certified, plus radiant barrier. The price vs effectivness of bubble wrap to fiberglass make bubble wrap a joke. after all its just bubble wrap.
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HAve you seen a conditioned crawl yet?
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Before insulating your ducts that run thru the crawl space you will want to seal them first -- duct mastic is considered best though I've used the foil tape to seal all the seams. I've used foil tape that has held up very well over ten years now. Don't use regular duct tape -- it doesn't last. Seal the seams of the heating ducts as well as the return air ducts.
I've used the fiberglass duct insulation by Manville that I picked up at Lowes.
After sealing my ducts in my crawl space and then insulating all the heating and air return ducts I noticed a big improvement in the air flow and the heat of the air from the registers as far as how much there are a lot of SWAG methods that others have talked about but I do know I'm saving now for the life of the house and since I did the work myself my only costs were materials and time.

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Are you wrapping the bubble wrap directly on the ductwork or are you putting an air space between the BW and the duct?
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Sorry for not being more explicit in describing my situation. The ducts are bare metal. I have cut sections of the insulation and wrapped them around the cylindrical duct pipes, sealing each section with aluminum tape. The insulation is called Reflectix. They claim to block up to 97% of radiant heat. They indicate different R values for various applications, but R-6 for bare ducts. I know from checking that when there is hot air flowing through the ducts, the bare uncovered portions are very warm to the touch, while the covered sections are barely warm to the touch. There is no air gap between the insulation and the pipes, but the inner 'bubble wrap' should provide some sort of trapped air barrier. I have done about 30% of the job and trying to decide to finish it, or not. We had very cold temperatures last few weeks in the Chicago area, but now the temperatures are moderating. My gas bill for December was almost double of what it was last year for the same number of consumed therms. This insulation sells for about $16 for a 16" by 25' roll, and so far I have used 2 rolls. I have not blocked the vents in my crawl because I want some air circulation in their to prevent mold, etc. The ceiling of the crawl is uninsulated, so some of the heat makes it's way through the floor to the first floor living space.
HeatMan wrote:

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Then you didn't do it correctly.
The Reflectix is supposed to have an air gap between the insulation and the duct. THAT'S what get's the wrap an R6.
The inner bubble wrap don't do anything.

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Reflextic, yes Ive seen that crap, as you read it says " like R6" just like insulating paint says its "like R" whatever. The key work is "Like" it is not a certified rating, don`t you even wonder why Reflextic has different " like" ratings for different applications. Get a Cerfified insulation, one that is industry accepted and known, Fiberglass. And best is something designed for your job.
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HeatMan wrote:

Are you sure? I thought the necessary air gap consisted of the air in the bubbles. Otherwise what's the point of the bubbles?
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Yes, I'm sure. The bubbles hold the air inside the air space.
Install one piece correctly and the other in the haphazard way you mentioned. Get a surface reading thermometer from Radio Shack(no, I don't have a link) and 'shoot' the insulation. I'll bet you see a warmer surface on the haphazard Reflectix.
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I have checked further with the web site of Reflectix, which I should have done in the first place. They claim their insulation gives about a 4.2 R value if applied with no air gap, as opposed to the R-6 value with a single air gap. This value goes up to an even higher value of about R-15 if a second layer with another air gap is applied.
I somewhat fault the company for showing nice pictures of the various ways this stuff can be used, but nothing about how to install it over ducting to get the best results. There are some instructions for crawl spaces, but nothing specific to ducts. All they had to do was point people to their web site where everything is explained quite clearly. Anyone can check the site yourselves at www.reflectixinc.com. That's another problem with buying at Builder stores. The prices are cheaper, but you seldom find anyone knowledgable about what they are selling. Hardware stores do much better, in this respect.
HeatMan wrote:

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With Reflectix, you only get the full R-value if you place spacers under the wrap - read the directions carefully. The spacers are to provide a layer of trapped air between the wrap and the ducts. You are probably achiving significantly less than R-6.5 if you didn't do this, but another option is to wrap the ducts twice around with the wrap. In the real world, I can tell you that in a similar situation, crawl with vents, uninsulated floor, my coldest room increased in temperature approx 2-3 degrees, which is significant but not mind blowing. In our case, it solved a sticky problem of two rooms which had had a ceiling vaulted without a proper increase in the heating mechanics. I do however question the wrapping of the return ducts. In that case, the temperature differential between the duct air and the surround air is quite a bit less than the supply duct air and the crawl air, and therefore the heat loss is less, and less can be accomplished by wraping. Cetainly the payback is much longer. I would also partially block the air vents in the winter. Conditions are so dry then from heating (in the crawl) that there should not be a problem, and you will reduce the effect of cold air blowing up under your floors. Only in the attic would I NOT block the vents, as your moist heated air rises to that level.
sherwindu wrote:

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